The invention relates to a device and a method for detection of gear position in an automotive gearbox. It is applicable in principle to any desired engine with associated gearbox, but the case hereinafter described to illustrate and exemplify the invention is that where such a device is arranged in a motor vehicle, more particularly in a bus or a truck.
For a number of different reasons it is important for an arrangement for controlling an engine which is adapted to powering a load in the driveline, i.e. the power transmission path, downstream from a gearbox, to have knowledge about the extent to which a gear position is established and which gear position it is. For example, a protection for a clutch arrangement for disengaging the gearbox from the engine only becomes disconnected when a gear position has been detected, with the result that the engine can then be controlled to deliver the torque which the vehicle driver or engine operator requires. This cannot take place until a gear position has been reliably detected.
In some transmissions, different gear positions may also tolerate different amounts of torque, in which case it is important to know, preferably as quickly as possible, which gear position the gearbox is in, in order to spare sensitive parts of the transmission.
Information about a gear position can also be used, e.g. as regards trucks, for weight estimation, i.e. for calculating how much a truck weighs. It is important that this be done during the acceleration phase, and it has been found that the most reliable results are achieved through measurements made when a gear position has just been reached, since this is the time when the torque delivered by the engine and acceleration can best be measured.
In all the above-mentioned cases it is desirable to detect as quickly as possible that a gear position obtains.
For detection of gear position in an automotive gearbox, there are known devices of the type based on detecting the respective speeds of the driveline upstream from the clutch and downstream from the gearbox and calculate a quotient of these speeds and comparing this quotient with values of such a quotient determined for each gear position of the gearbox. It is thus decided that a gear position obtains if for a predetermined period of time this quotient is between upper and lower limits about the quotient value pertaining to the respective gear position.
Such a device is previously known, e.g. from U.S. Pat. Nos. 5,921,135 and 4,320,381. Even if those devices function reliably, it is desirable, for the reasons indicated above, to increase their speed and also, if possible, the reliability of their detection of gear position.
The former is of particular importance in the case of a motor vehicle, since the driver may be irritated by having to wait for a clutch protection to be disengaged, e.g. when starting the vehicle.
It should be noted that the invention is directed at detection of gear positions in automotive gearboxes which comprise a so-called split gear for defining at least two gear positions, so-called split positions, relating to each gear position otherwise defined by the gearbox.